To see your teacher (past or present) in your dream suggests that you are seeking some advice, guidance, or knowledge. You are heading into a new path in life and are ready to learn by example or from a past experience.
Consider your own personal experiences with that particular teacher. What subject was taught? Alternatively, a teacher relates to issues with authority and seeking approval. You may be going through a situation in your waking life where you feel that you are being treated like a student or in which you feel you are being put to a test. Also pay attention to the demeanour and attitude of the teacher in your dream. If the teacher in your dream is mean, then it implies that you may be putting too much pressure on yourself to succeed.
To dream that you are a teacher indicates that you are in a position of disseminating your knowledge and wisdom to others. The dream may imply how you are “teaching someone a lesson” and giving them a hard time about something. If you are a teacher in real life, then the dream is just a reflection of who you are and is about your work.